1. Field of the Invention
The present invention relates to a lamp driving device and, more specifically, to a lamp driving device which is effective for detecting an abnormal electrical discharge.
2. Description of the Related Technology
In the lamp driving device that illuminates a lamp upon generation of high voltage, there is a case in which the abnormal electrical discharge due to bad electrical contact of a transformer or the lamp. Since the abnormal electrical discharge of this type may cause smoking or ignition, it is necessary to stop a lighting operation in case of abnormal electrical discharge.
Several methods of detecting the abnormal electrical discharge and stopping the operation are disclosed, for example, in Japanese Patent No. 3123161, JP-A-2002-151287 and JP-A-2004-135489.
Japanese Patent No. 3123161 discloses a method of detecting the abnormal electrical discharge using a capacitor as shown in FIG. 1 in the same document, JP-A-2002-151287 discloses a method of detecting the abnormal electrical discharge using a high-pass filter as shown in FIG. 2 in the same document, and JP-A-2004-135489 discloses a method of detecting the abnormal electrical discharge using a flux variation.
However, with the methods shown in Japanese Patent No. 3123161 and JP-A-2002-151287, since a resistor for voltage transduction of signals detected by the capacitor or the high-pass filter is necessary, the number of parts increases. With these methods, signal components at high frequency are detected substantially the entire region, for example, malfunction may be resulted due to the influence of mobile phones.
In the method disclosed in JP-A-2004-135489, since wiring design for performing magnetic flux detection is necessary, the freedom degree of wiring on a substrate is reduced, and selectivity of frequency is not good. Therefore, there is a possibility of malfunction due to the influence of the mobile phone as in the cases of Japanese Patent No. 3123161 and JP-A-2002-151287.
There is a problem common to these three patent documents that even when noise elements other than the abnormal electrical discharge, for example, electrostatic discharge is occurred, the noise elements pass through the capacitor and the high-pass filter, and hence the operation may be stopped under the circumstances in which the operation should not be stopped.